Electrical wave analyzer



Dec. 9, 1947. c. G. soN'rHElMER LECTHICAL WAVE ANALYZER d. mu-

Bnventor SonTHElmER Emu Gttorncg Patented Dec. 9, 1947 @will MH ttijct UNITED STATES PATENT OFFICE ELECTRICAL WAVE ANALYZER Carl G. Sontheimer, Haddoneld, N. J., assignor vto Radio Corporation of America, a corporation of Delaware Application September 25, 1943, Serial No. 503,841

6 Claims. l

` This invention relates'generally tovwave analyzers and more particularly to apparatus for analyzing the relative magnitudes and frequencies of signal voltages derived from electrical circuits.

Heretofore, current analyzers for measuring the tudes of the selected frequency components.

Measurements with apparatus of this type necessarily involve numerous` apparatus adjustments to determine the relative frequency-amplitude characteristics of thel signals being observed. Also, the particular characteristics of the filter networks throughout the frequency band to be observed must be taken into consideration in the final analysis of the signal components.

The instant invention contemplates an improvement upon known systems for analyzing currents in that tuned lter .networks are not required since vthe particular frequency component is selected by means of an adjustable oscillator which is lconnected to activate a balanced modulator circuit responsive to thesignal energy under observation.

In the-simplest embodiment of the invention,

a circuit under testis connected to a balanced modulator circuit which normally is so biased that no signals will be transmitted thereby. A variable frequency oscillator is connected through an adjustable phasing circuit to a symmetrical point inthe balanced modulated circuit whereby no output therefrom is derived from thevariable oscillator, but signals from the circuit under test which correspond in frequency to the oscillator frequency are transmitted by the balanced modulator and applied to an indicating circuit. Y

A second embodiment of the invention is especially adapted to the measurement of the relative amplitudes of selected harmonics of the output of an'amplier, to the input of which a sine wave signal is' supplied. In this embodiment a test frequency source, having substantially sine wave output, is connected to the input of an amplier of -which the harmonic distortion is to be measured. The output'circuit of the amplifier f is connected to the input circuit of a balanced circuit to synchronize an adjustable lockingoscillator Vcircuitwhich may be locked at the fundamental or at successive harmonics of the test frequency. The output circuit of the adjustable locking oscillator is connected through an adjustable phasing circuit to a symmetrical point in the balanced modulator.v No output is derived z-from the balanced modulator in response to the signals applied thereto from the adjustable locking oscillator. However, signals applied to the modulator from the. adjustable locking oscillator permit the transmission therethrough of signals of the same frequency derived from the amplifier under test. The signals thus transmitted by the balanced modulator are applied to a suitable measuring circuit for indicating the relative amplitudes of the harmonics selectedvby the locking oscillator.

Among the objects of the invention are to provde an improved method of ,and means for analyzing the relative amplitudes and frequencles of signals derived from an electrical circuit. Another object of the. invention .is to provide an improved method of and means,. for analyzing the relative harmonic distortion Iin an electrical circuit under test. `An additional object of the invention is to provide an improved method of and means for measuring the relative vamplitudes and frequencies of signal voltages derived from an electrical circuit wherein particular frequencies to be observed are derived from a local oscil- 4lator and applied to abalanced-modulator circuit rived from an electrical circuit which comprises a second signal source of. adjustable frequency and phase for activatingla normally-biased-off balanced modulator circuit to measure the amplitudes of selected frequencies from the circuit under test.

The invention will be further described by reference to the accompanying drawingbf which Figure 1 is a schematic circuitfdiagram of one embodiment thereof, and Figure 2 is a schematic circuit diagram of a second embodiment of the invention. Similar reference characters are applied to similar elements throughout the drawing.

Referringjto Figure'fl. anelectrical circuit I of which the relative amplitudes and frequencies of signals derived'therefrom is to be measured, is connected to a primary Winding] of a iirst transformer 3. The ytransformer .3 includes a vides Astrong harmonic frequency output.

center tapped secondary winding 4, the end terminals of which are connected respectively to the control electrodes of two balanced modulator thermionic tubes 5, 6. The cathodes of the two modulator tubes 5, 6 are connected together and grounded.

`A source of control electrode bias such as, for example, a battery 'I is connected between the cathodes of the balanced modulator tubes 5, 6 and one terminal of the secondary winding 8 of a second transformer 9. The remaining terminal of the secondary winding 8 of the second transformer 9 is connected to the center tap of the secondary winding 4 of the first transformer 3.

A variable frequency oscillator IIJ, having a frequency range equal to the frequency range to be observed from the circuit under test, is connected through an adjustable phase control circuit II to the primary winding I'2 of the second transformer 9. The anodes of the balanced modulator tubes 5, 6 are connected to the end terminals of a center tapped primary winding I3 of an output transformer I4. A source of positive anode potential is connected to the center tap of the primary winding I3 of the output transformer I4.

A secondary winding I5 of the output transformer -I4 is connected, for example, through a rectifier I6 and an integrating circuit comprising a vcapacitor I'I and a resistor I8 to anv indicating `the measuring circuit which includes the indicating meter I9. The'reading onthe indicating meter I9 will be characteristic of the relative amplitude of each particular frequency component selected by the variable'frequencyoscillaton Figure 2 is a circuit especially-adapted to the measurement of harmonic distortion produced within the circuit or device under test. The device to be tested is excited by a test frequency source having substantially sine wave output. The test frequency source'ZI, having a sine wave output at a predetermined xed frequency, is connected to the input of an amplifier or other cir- I monic generators, synchronization of locking oscillators and phase controls are described, for example, in Radio Engineers Handbook, by F. E. Terman (1943), at pages 458 etseq., 510 et seq., and 949 et seq., and in the extensive bibliography referred to therein. The characteristics of these devices for the purposes set forth may be selected :in accordance with known technique. The transformers 3 and 9 are connected in a balanced mod- -ulator circuit comprising the thermionic tubes 5, 6 in the same manner as described heretofore in the circuit of Figure 1. Similarly, the output of the balanced lmodulator is connected to an indicating meter I9 in the same manner as described heretofore.

In operation, the test frequency source is adjusted to the desired test frequency, and the adjustable locking oscillator is rst adjusted to be locked in at the fundamental frequency of the test frequency source. The phase control I I is adjusted until a maximum indication is derived on the meter I9'. vThe adjustable locking oscillator is successively adjusted to be locked in at successive harmonics of the test frequency. After each :adjustment of the locking oscillator the phase control II is adjustedto provide a maximum indication on the output meter I9. The successive readings provided by the output meter I9 are characteristic of the relative magnitudes of the fundamental and harmonic frequencies transmitted by the amplifier under test in response to the substantially sine Wave input test frequency.

The phase control circuit II should be adjustable over a 90,phase range. The adjustable oscillator employed in both modifications of the in'. vention should be substantially free of harmonic distortion since any such distortion will provide spurious indications upon the-output meter I9. It should be understood that .any -type of balanced modulator circuit known in the art, which will transmit signals from the circuit under test only in response to signals of likev frequency derived from the adjustableos'cillator, may be employed to provide the desired output indications. This condition obtains when the negative bias provided by the grid bias battery for the modulator tubes preferably exceeds the tube anode current cut-off grid bias by an amount substantially equal to the voltage magnitude of the signals to be measured. Thus the modulator tubes conduct only when the oscillator output reduces the grid bias to a value such that the applied signals will be c-uit 22 which' is tobe tested. The output circuit of the amplifier 22 is connected tothe primary winding 2 of a firsttransformer 3 in the same manner as described in Figure 1. The output circuit of the test frequency source is also connected to the input of a distortion circuit such as, for example, a distortion amplifier 23 which pro- The output of the distortion amplifier 23 is applied to an. adjustable locking oscillator 24 which may be locked in at the fundamental or any desired "harmonic `of the output frequency derived from t'he `test frequency source 2|.' l It isv well known 1. `that thermionic tube oscillators may be locked" .to an inputfrequency source, or to a harmonic with. TheI output currents of the adjustable lock- Qing oscillator 24 are applied, through an adjustable phase control network. Il, to the primary winding I2 of a second transformer 9. The design characteristics of distortionampliers as harrectified. Dueto the conventional input and output balanced signal circuits, the oscillator signals are balanced out in the modulator output circuit,

While the selected signal to be analyzed is applied wave output Voltage, means for applying saidl voltage to actuate said amplifier, a, distortion circuit, means -for applying said voltageto actuate said circuit to provide high harmonic output components therefrom, a locking oscillator, means connecting said circuit to said oscillator to provide oscillations at a predetermined one of said frequencies derived from said circuit, a balanced modulator, means connecting said amplifier to @RMN Lvl! HUUHP actuate said modulator, means connecting said oscillator to said modulator to activate said modulator to pass substantially only signals derived from said amplifier which correspond in frequency to said predetermined oscillator frequency, and means responsive to said passed modulator'signals for indicating the magnitude of said predetermined one of the harmonic frequency components of the signals derived from said amplifier.

2. Apparatus of the type described in claim 1 including means for adjusting the frequency of said oscillator to different predetermined harmonic frequencies of said reference frequency for indicating the relative harmonic frequency magnitudes of signals derived from said amplifier.

3. Apparatus of the type described in claim 1 including means for adjusting the relative phases of said signals derived from said amplifier and said oscillator.

4. Apparatus for measuring the' harmonic distortion of an amplifier including a reference frequency voltage source having a s antiall ,sine W2llf 9.uiput1s2lg am.gans,for applying Said voltage to actuateuslaid amplifier, a distortion circ'uit'fiiieans for applying said vo1t age to actuate said circuit to provide high harmgnicoutputnom- POnenS therefrom, a lglqngwoscillator, means connecting said circuit tomsaid oscillator tol provide oscil'`12tizsatapredetermined onef said frequencies derived from s aidcircuit, a, balanged mqdulatcrromprising s Pair. efthernlionc tuiles connected in a balanced circuit and normally biased to anode current cut-o ff..condition,y pushpull means connecting said amplifier to actuate said modulate""means'connecting said oscillator to said "mdulatoijtol activate' 'said' "modulator to pas's'"sbstantially only signals derived from said amliiier which correspond in frequency to'v ponents of the signals derived from said amplifier.

5. Apparatus for analyzing the relative component amplitudes and frequencies of complex multifrequency signals derived frol n an el ec`trggl circuit comprising a source of signals connected `to said circuit, a source of oscillations adiustable in frequency and phase to the 'frequency and phase of a selected frequency component of said derived complex signals, a balanced modulator, biasing voltage means for said modulator normally blocking transmission of said complex signals through said modulator, means connecting said source of oscillations to said modulator to unblock said modulator to pass only said selected component of said derived complex signals which corresponds in frequency and phase to said adjusted oscillations, and means for deriving from said modulator output signals of magnitude which is proportional to the magnitude of said selected component of said complex signals derived from said electrical circuit.

6. Apparatus according to claim 5 including an indicator responsive to said derived output signals.

CARL` G. SONTHEIMER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,695,047 Horton Dec. 11, 1928 1,762,160 Curtis June 10, 1930 1,684,403 Mason Sept. 18, 1928 1,527,228 Schelleng Feb. 24, 1925 1,596,942 Nyquist et al Aug. 24, 1926 1,854,432 Thurston Apr. 19, 1932 1,645,618 Nyquist Oct. 18, 1927 1,755,244 Kietze Apr. 22, 1930 2,093,512 Bowen Sept. 21, 1937 

